TETRAMETHYLENECYCLOBUTANE

1,2,3,4-tetramethylenecyclobutane is a molecule with a HOMO-LUMO gap, in which the HOMO is doubly occupied but the LUMO is unoccupied. It is a stabilized singlet molecule. You can rearrange the squaroexocyclobutadieneite pattern into an alternative pattern comprised of tetramethylenecyclobutane substructures. Just by rotating around, at a right angle, the 1,3-dimethylenecyclobutane units in the "squaro" lattice. I am not sure if the rest of the single C-C bonds form a stable lattice, but I think they might. It might be an especially stable alternative pattern to the "squaro" version because of the relative stability of the tetramethylenecyclobutane substructures.